Briquetting rolls are used to briquette powders and granules such as ironmaking dust or product scraps, so as to produce a briquette shape with a view to facilitating reuse. That is to say, briquetting rolls are rolls having multiplicity of pockets (indentations) formed in the outer circumferential surface, and two rolls are arranged in parallel at positions vertically or horizontally close to each other, and driven in rotation in opposite directions to each other (see FIGS. 1A and 1B). The powders and granules are supplied as raw materials between the two briquetting rolls, so as to produce a briquette having a shape corresponding to the shape of the pockets.
Patent Literatures relating to briquetting rolls include, for example, the following PTL 1.
In general, briquetting rolls are made by shrink fitting an annular sleeve on the outer circumference of a drum (large diameter part) in the middle of a shaft made of steel. For briquetting rolls that handle ironmaking dust and the like, conventionally, the sleeve is generally formed from a single material (single layer structure) which is high-speed tool steel (SKD 61) or high-chromium cast iron. Sleeves made of these materials are cast by centrifugal casting or ordinary static casting, then heat treatment is carried out to maximize the hardness, whereafter the pockets are machined by electric discharge machining. Such a sleeve is integrated with the shaft by shrink fitting, to be used as a briquetting roll.
In cases such as when handling hard powders and granules or when hard foreign matter is included or the like, spalling (breaking) may occur in the vicinity of the surface of the roll, and the pockets often become shallow due to early wear. Briquetting rolls must, therefore, have sufficient mechanical strength. In particular, it is desirable to increase the fracture toughness value, so as to impart spalling resistance, and to increase hardness, so as to increase abrasion resistance.
With an integral type sleeve, the entire unit becomes unusable if spalling occurs locally. To avoid this, the sleeve is sometimes configured in a divided type (a sleeve resulting from combining a plurality of segments is used in place of an integral sleeve).